, magazine=(American Scientist), title= In the News
, passage=Oxygen' levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis: the ability to convert water and carbon dioxide into carbohydrates and waste ' oxygen using solar energy. The evolutionary precursor of photosynthesis is still under debate, and a new study sheds light.}}

(medicine) A mixture of oxygen and other gases, administered to a patient to help him or her to breathe.